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Wind directly forces inertial oscillations in the mixed layer. Where these currents hit the coast, the no-normal-flow boundary condition leads to vertical velocities that pump both the base of the mixed layer and the free surface, producing offshore-propagating near-inertial internal and surface waves, respectively. The internal waves directly transport wind work downward into the ocean’s stratified interior, where it may provide mechanical mixing. The surface waves propagate offshore where they can scatter over rough topography in a process analogous to internal-tide generation. Here, we estimate mixed layer currents from observed winds using a damped slab model. Then, we estimate the pressure, velocity, and energy flux associated with coastally generated near-inertial waves at a vertical coastline. These results are extended to coasts with arbitrary across-shore topography and examined using numerical simulations. At the New Jersey shelfbreak, comparisons between the slab model, numerical simulations, and moored observations are ambiguous. Extrapolation of the theoretical results suggests that [Formula: see text](10%) of global wind work (i.e., 0.03 of 0.31 TW) is transferred to coastally generated barotropic near-inertial waves.
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This content will become publicly available on June 1, 2026
Breaking Internal Waves on Sloping Topography: Connecting Parcel Displacements to Overturn Size, Interior-Boundary Exchanges, and Mixing
Internal waves impinging on sloping topography can generate mixing through the formation of near-bottom bores and overturns in what has been called the “internal swash” zone. Here, we investigate the mixing generated during these breaking events and the subsequent ventilation of the bottom boundary layer across a realistic nondimensional parameter space for the ocean using three-dimensional large-eddy simulations. Waves overturn and break at two points during a wave period: when the downslope velocity is strongest and during the rapid onset of a dense, upslope bore. From the first overturning bore to the expulsion of fluid into the interior, there is a strong dependence on the effective wave height, a length scale defined by the ratio of wave velocity over the background buoyancy frequency, an upper bound on the vertical parcel displacement an internal wave can cause. While a similar energetically motivated vertical length scale is often seen in the context of lee-wave generation over topography, the results discussed here suggest this readily measurable parameter can be used to estimate the size of near-boundary overturns, the strength of the ensuing turbulent mixing, and the vertical scale of the along-isopycnal intrusions of fluid ejected from the boundary layer. Examining a volume budget of the near-boundary region highlights spatial and temporal variability that must be considered when determining the water mass transformation during this process.
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- Award ID(s):
- 2232441
- PAR ID:
- 10618194
- Publisher / Repository:
- Journal of Physical Oceanography
- Date Published:
- Journal Name:
- Journal of Physical Oceanography
- Volume:
- 55
- Issue:
- 6
- ISSN:
- 0022-3670
- Page Range / eLocation ID:
- 645 to 661
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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